The present invention relates to the field of inkjet printers and discloses an inkjet printing system which includes a bend actuator connected to a paddle for the ejection of ink through an ink ejection nozzle. In particular, the present invention includes a thermally actuated ink jet including a tapered heater element.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al) Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, by Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 which discloses a piezoelectric push mode actuation of the ink jet stream and by Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and by Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned reference ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture in communication with the confined space onto a relevant print media. Printing devices utilizing the electrothermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction, operation, durability and consumables.
In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined in the following paragraphs.
Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon the standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are more well known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, gallium arsenide etc. Hence, it is desirable, in any MEMS construction, to utilize well proven semi-conductor fabrication techniques which do not require the utilization of any xe2x80x9cexoticxe2x80x9d processes or materials. Of course, a certain degree of trade off will be undertaken in that if the use of the exotic material far outweighs its disadvantages then it may become desirable to utilize the material anyway.
With a large array of ink ejection nozzles, it is desirable to provide for a highly automated form of manufacturing which results in an inexpensive production of multiple printhead devices.
Preferably, the device constructed utilizes a low amount of energy in the ejection of ink. The utilization of a low amount of energy is particularly important when a large pagewidth full color printhead is constructed having a large array of individual print ejection mechanisms with each ejection mechanism, in the worst case, being fired in a rapid sequence.
There is disclosed herein an ink jet nozzle assembly including a nozzle chamber and a nozzle, the chamber including a movable portion and a pair of actuating arms connected to or formed integrally with the movable portion and functioning in use to selectively move said movable portion to eject ink from the chamber via said nozzle, the actuating arms having equivalent thermal expansion characteristics so as to avoid differential thermal expansion in response to changes in ambient temperature.
Preferably the actuating arms are formed of materials having equivalent thermal expansion characteristics and a current is passed through one only of the actuating arms to effect said movement.
Preferably said nozzle chamber has an inlet in fluid communication with an ink reservoir;
the chamber includes a fixed portion configured with said movable portion such that relative movement in an ejection phase reduces an effective volume of the chamber, and alternate relative movement in a refill phase enlarges the effective volume of the chamber;
the actuating arms are spaced apart and are adapted for selective differential thermal expansion upon heating so as to effect said relative movement; and
the inlet is positioned and dimensioned relative to the nozzle such that ink is ejected preferentially from the chamber through said nozzle in droplet form in the ejection phase, and ink is alternately drawn preferentially into the chamber from the reservoir through the inlet in the refill phase.
Preferably the movable portion includes the nozzle and the fixed portion is mounted on a substrate.
Preferably the actuating arms effectively extend between the movable portion and the substrate.
Preferably the fixed portion includes the nozzle mounted on a substrate and the movable portion includes an ejection paddle.
Preferably the actuating arms effectively extend between the substrate and the ejection paddle.
Preferably the actuating arms are located substantially within the chamber.
Alternatively the actuating arms are located substantially outside the chamber.
Preferably the fixed portion includes a slotted sidewall in the chamber through which the actuating arms are connected to the movable portion.
Preferably the actuating arms are of substantially the same cross-sectional profile relative to one another.
Alternatively the actuating arms are of different cross-sectional profile relative to one another.
Preferably the arms are of substantially the same material composition relative to one another.
Alternatively the arms are of different material composition relative to one another.
Preferably the arms are substantially parallel to one another.
Alternatively the arms are substantially non-parallel to one another.
Preferably one arm is adapted to be heated to a higher temperatures than the other arm in order to effect thermal actuation.
Preferably the respective arms are formed from multiple layers of different material compositions disposed such that thermal expansion or contraction in one arm due to the ambient temperature fluctuations is balances by a substantially corresponding thermal expansion or contraction in the other arm.
Preferably the assembly is manufactured using micro-electro-mechanical-systems (MEMS) techniques.
Preferably an electric current is passed through one said actuating arm and not the other said actuating arm in use.